Conventionally, double-sided indexable cutting inserts having eight main cutting edges and eight wiper edges have been used when machining a shoulder in a workpiece. When machining a shoulder in a workpiece by means of such a cutting insert, one main cutting edge and one wiper edge, which are located in two adjacent side faces of the cutting insert, are used. However, other cutting edges do not need to contact the workpiece.
FIG. 1 shows a prior art cutting insert 101. FIG. 2 shows a cutting tool 102 on which the cutting insert 101 is mounted. When the cutting insert 101 is mounted on the cutting tool 102 as shown in FIG. 2, an operative main cutting edge 112 and an operative wiper edge 116 cut a shoulder in a workpiece. To position a non-operative main cutting edge 118 away from a base wall of the shoulder, the cutting insert 101 is mounted on the cutting tool 102 as being rotated by approximately 1° around an axis perpendicular to a base surface of an insert pocket of the cutting tool 102. As a result, an upright wall of the shoulder cut by the cutting insert 101 forms an angle of approximately 89° with the base wall of the shoulder. Thus, the cutting insert 101 and the cutting tool 102 shown in FIGS. 1 and 2 cannot cut a right-angled shoulder in a workpiece. Further, if the depth of the shoulder to be cut is greater than a predetermined depth of cut D1, then a non-operative wiper edge 114 contacts the upright wall of the shoulder. Thus, the cutting insert 101 and the cutting tool 102 shown in FIGS. 1 and 2 cannot be used for cutting a shoulder having a depth greater than the predetermined depth of cut D1.
FIG. 3 shows another prior art cutting insert 201 disclosed in Korean Laid-Open Patent Publication No. 2010-0015837. FIG. 4 and FIG. 5 show a cutting tool 202 on which the cutting insert 201 shown in FIG. 3 is mounted. The cutting insert 201 has main cutting edges 204 and wiper edges 206. The height of the wiper edge 206 becomes greater as it goes away from a junction 208 with the main cutting edge 204. To ensure a relief angle during cutting operations, the cutting insert 201 is mounted on the cutting tool 202 as being rotated around an axis perpendicular to a base surface of an insert pocket of the cutting tool 202 and further being inclined with respect to a rotary axis RA of the cutting tool 202. Accordingly, when the cutting insert 201 mounted on the cutting tool 202 is viewed from front (see FIG. 5), a non-operative wiper edge 214 projects further outwardly of the cutting insert 201 than an operative main cutting edge 212. That is, as shown in FIG. 5, the non-operative wiper edge 214 forms an angle of approximately 88° with the base wall of the shoulder of the workpiece. When cutting a shoulder in a workpiece by means of such a cutting insert 201, the operative main cutting edge 212 and the operative wiper edge 216 can cut a right-angled shoulder only up to a predetermined depth of cut D2. When cutting a shoulder at a depth greater than the predetermined depth of cut D2, the non-operative wiper edge 214 contacts the upright wall of a shoulder. Thus, the aforementioned prior art cutting insert 201 cannot be used for cutting a right-angled shoulder having a depth greater than the predetermined depth of cut D2.
As such, the prior art cutting inserts and the cutting tools with such cutting inserts cannot cut a right-angled shoulder. Even if a right-angled shoulder can be cut by those cutting inserts and cutting tools, it can be cut only up to a limited depth.